Yes, 400 teams will slow you down a lot.
I have a top end computer I bought last year.
With a 30 team league, full minors I can whiz through seasons.
With a test league of over 350 teams it drags. That's a lot of data to process and write.
Nothing wrong with the game/computer, it's just the size.
And if you think it's slow now, wait another 10 or so seasons.
